Sir.—I recently reviewed the article by Naqvi et al,1 "Vancomycin Pharmacokinetics in Small, Seriously Ill Infants." In their analysis of serum vancomycin levels, the authors employed a one-compartment model using the equations of Sawchuk and Zaske.2 This technique of calculating the elimination rate constant, volume of distribution, and clearance will be in error when the drug exhibits multicompartment characteristics.3

Vancomycin has been shown to follow a biexponential decline in serum concentrations following intravenous administration in both adults and children.4,5 Naqvi et al sampled peak vancomycin concentrations immediately following a 60-minute infusion. Based on data reported by Schaad et al,5 which indicated distribution half-lives in infants of 0.05 to 0.5 hours, a significant amount of vancomycin may be in the central compartment at the end of the infusion.5 At this time point, serum concentrations are rapidly falling in the central compartment due to both